Generally, in a wire-cut electrical discharge machine, a pair of upper and lower wire guides is used to tension the wire electrode, with the lower wire guide positioned below the workpiece. Discharge energy is applied to the wire electrode while supplying machining fluid to the gap formed by the workpiece and the wire electrode, thus wire-cut discharge machining the workpiece. Such wire-cut electrical discharge machines include, for example, the "submersion-type" wire-cut electrical discharge machines, in which wire-cut electrical discharge machining can be performed with the workpiece submerged in the machining fluid within a work tank. In this type of wire-cut electrical discharge machine, when performing electrical discharge machining on a workpiece submerged in the machining fluid within a work tank, the movement of the lower arm which supports the lower wire guide is limited by the side wall of the work tank. As a result, the range of movement of the lower wire guide becomes extremely narrow, and the dimensions of the machinable workpiece with respect to the dimensions of the work tank are reduced, requiring tanks which are quite large in comparison to the size of the machinable workpiece. This is the primary factor preventing the size reduction of wire-cut electrical discharge machines. The same problem arises when wire-cut electrical discharge machining the workpiece either while directly flushing the machining gap with machining fluid or while submerging the gap in machining fluid. A wire-cut electrical discharge machine amenable to size reduction is proposed as a solution to the above described problems in Japan Laid Open Patent Publication 60-52223, whereby a mechanism is provided to enable the movement of the lower arm along the long walls of the work tank while permitting the lower arm to penetrate the work tank side wall. In a wire-cut electrical discharge machine of the above-described configuration, in which the lower arm penetrates one of the work tank side walls, the difference between the work tank dimensions and the maximum machinable workpiece dimensions can be reduced. However, absolutely smooth movement of the lower arm is hindered by the sealing device placed between the lower arm and the work tank side wall, which is used to prevent leakage of machining fluid. The sealing device tends to apply a lateral force due to the movement of the lower arm with respect to it, producing the problem of reduced machining accuracy. Also, in that type of sealing mechanism, the sealing member can easily become degraded by the rubbing effect associated with lower arm movement, requiring frequent maintenance and inspection, creating a separate problem of new costs associated with the maintenance and inspection needed to maintain a given performance over time.